Electrolytic generation of nitrogen using azole derivatives

ABSTRACT

The invention provides electrolytes for the electrochemical generation of nitrogen gas by anodic oxidation of triazole and tetrazole derivatives. Electrolytic cells incorporating these electrolytes are also disclosed. The nitrogen gas so produced may be useful to actuate mechanical transducers in fluid dispensers.

FIELD OF INVENTION

The invention is in the field of methods for electrochemical generationof gases. More particularly this invention relates to the generation ofnitrogen gas from triazole and tetrazole derivatives, and mechanicaltransducers actuated by the nitrogen gas so produced, particularly inthe field of fluid dispensers.

BACKGROUND OF THE INVENTION

The controlled electrolytic generation of gases is useful to convertchemical to mechanical energy in a variety of applications. For example,a variety of lubricant or fluid delivery systems driven by theelectrolytic generation of a gas are known. For example, U.S. Pat. No.4,023,648 to Orlitzky et al. (1977) shows a lubricant applicator drivenby gas generated in an electrochemical cell and provides a method forthe electrochemical generation of hydrogen gas.

Fluid dispensers driven by electrochemically generated gases, and otherelectrochemical transducers may often be used in circumstances whichgive rise to special operational requirements. Typically, components ofany electrolytic cell used in such an application must be stable overtime and over a range of temperatures. In such devices, it may beundesirable to have highly reactive gases generated, such as hydrogen oroxygen. Once the circuits are closed to initiate electrolytic gasgeneration, it is generally desirable to have relatively fast electrodereactions with low overpotential (i.e. a small difference between theelectrode potential under electrolysis conditions and the thermodynamicvalue of the electrode potential in the absence of electrolysis), smallconcentration polarisation of solutes across the cell (i.e. rapiddiffusion of reactants to the electrode surfaces), and small separatorresistance effects (i.e. little resistance caused by solid separatorswithin the cell. It is also desirable to produce gases from a smallamount of material, i.e. to have efficient gas generation and highstoichiometric coefficients for gaseous reaction products.

The electrochemical generation of a gas can be represented by equation(1):aR+/−ne ⁻ →bG+cPwhere R, G and P represent the reactant, the gas product, and thenon-gas product respectively; and a, b, c, and n are the stoichiometriccoefficients. When utilizing an electrical circuit to drive the currentthrough the electrochemical cell it is desirable to produce gas in anefficient manner from a viewpoint of electric charge consumption. Suchefficiency requires a high gas product stoichiometric coefficientassociated with a low electron stoichiometric coefficient. Astoichiometric efficiency of gas generation (E) in moles per Faraday maybe defined in equation (1) as:E=b/n mol/F

Hydrogen and oxygen gases are used in a variety of known electrochemicalgas generators. For example the anodic oxidation and cathodic reductionof water respectively generate oxygen and hydrogen by the reactions 1and 2:Anodic oxidation of H₂O: 2H₂O−4e ⁻→O₂+4H⁺  reaction 1Cathodic reduction of H₂O: 2H₂O+2e ⁻→H₂+2OH⁻  reaction 2

The anodic oxidation of water has a low stoichiometry efficiency for gasproduction (0.25 mole of oxygen gas per Faraday). A low stoichiometryefficiency may be undesirable because the quantities of reactant andcurrent needed to produced the desired amount of gas may require a largevolume of the unit and a high capacity energy source. Anotherdisadvantage of oxygen is that it may pose safety problems when utilizedfor dispensing combustible fluids such as grease.

The cathodic reduction of water has a better stoichiometric efficiencyfor gas production (0.50 mole of hydrogen gas per Faraday) but theproduction of hydrogen gas is hazardous due to its explosive reactivitywith oxygen upon ignition. Another disadvantage of hydrogen is that itdiffuses relatively rapidly through a variety of polymeric barriers thatmight otherwise be used to contain the electrolytically generated gas ina mechanical transducer, such as a fluid dispenser.

Nitrogen is a relatively inert gas that may usefully be produced byelectrolytic reactions to provide controlled amounts of gas. U.S. Pat.No. 5,567,287 issued to Joshi et al. (1996) discloses a solid stateelectrochemical nitrogen gas generator for fluid dispensing applicationswherein nitrogen is produced by electro-oxidation of alkali metalnitrides or azides. The azide half-cell reaction in that system producesnon-reactive nitrogen with a stochiometry efficiency of 1.5 moles ofnitrogen gas per Faraday (reaction 3).2N₃ ⁻→3N₂+2e ⁻  reaction 3

Based on reaction 3, a fluid dispenser operating at 0.25 mA has thepotential to generate about 0.33 ml STP of gas per hour for up to 4000hours from a battery with capacity of 1 A.h. With sodium azide as theanode reactant, 1 litre STP of nitrogen gas could be generated fromabout 2 grams of NaN₃.

The azide half-cell reaction in such a system may however be slow, inpart because of the high overpotential required for theelectro-oxidation of azide. To overcome the problem of the sluggishkinetics of the azide half-cell, additives such as thiocyanate may beused to catalyse iodine mediated formation of nitrogen from azides.However, such systems suffer from the disadvantages that azides aretoxic and the thiocyanate salt catalysts are also toxic. The presence oftoxic compounds may make it difficult to dispose of a device whichgenerates nitrogen gas from azides.

U.S. Pat. No. 6,299,743 to Oloman et al. (2001) discloses theelectrochemical generation of nitrogen gas from organic nitrogencompounds, such as hydrazides (RCONHNH₂), the corresponding organichydrazino-carboxylates (RCO₂NHNH₂) and amino-guanidine salts (e.g.aminoguanide bicarbonate H₂NNHC(NH)NH₂.H₂CO₃). For example, theelectro-oxidation of methyl hydrazinocarboxylate generates nitrogen gaswith a stoichiometric efficiency of 0.5 moles per Faraday according tothe putative reaction 4:CH₃CO₂NHNH₂—>CH₃CO₂H+N₂+2H⁺+2e ⁻  reaction 4

Based on reaction 4 an electrical source with a current of at least 0.75mA would be required to generate 0.33 ml STP/hour of nitrogen and a massof 4 gram of methyl hydrazino-carboxylate would be needed to produce 1litre STP of the gas.

Compounds having a high nitrogen content such as triazoles andtetrazoles have been investigated as non-azide nitrogen gas generantcomponents in pyrotechnic compositions that may be useful as propellantsor for inflating aircraft or automobile safety crash bags. Clearly, theexplosive release of gases is not desirable in controlled electrolyticgas generators.

SUMMARY OF THE INVENTION

In one aspect, the invention provides electrolytes for theelectrochemical generation of nitrogen gas by anodic oxidation of azolederivatives having a high nitrogen content. A high nitrogen contentazole compound or derivative refers, in some embodiments, to afive-membered N-heterocycle containing two double bonds and having atleast three nitrogen ring atoms. In alternative embodiments, the highnitrogen content azole derivatives of the invention may includetriazoles, aminotriazoles, tetrazoles, aminotetrazoles and their salts.A variety of triazoles and tetrazoles may be used and empirically testedfor performance in alternative embodiments.

The triazoles may include, for example, the 1H- and 2H-1,2,3-triazoletautomers, the 1H- and 4H-1,2,4-triazole tautomers, and their mono-, di-or trisubstituted derivatives. The mono-, di-, and trisubstitutedderivatives may include, for example, suitable alkyl, alkenyl, alkynyl,arylalkyl or aryl groups. The alkyl, alkenyl, and alkynyl groups may belinear or branched, substituted or unsubstituted. In some embodiments,the mono-, di-, and trisubstituted derivatives may include lower alkyl,lower aryl and arylalkyl groups. Lower alkyl and lower arylalkyl groupsdenote alkyl groups and alkyl moiety in arylalkyl groups having up toand including 4 carbon atoms. Lower alkyls may, for example, include,methyl, ethyl, propyl, isopropyl, butyl, isobutyl, secondary butyl ortertiary butyl. Lower arylalkyl may include, for example, benzyl. Arylgroups, for example, may include phenyl and phenyl substituted by up toand including 3 lower alkyl groups as defined above.

The aminotriazoles may include, for example, 1-amino-1H-1,2,3-triazole,2-amino-2H-1,2,3-triazole, 4-amino-1H or 2H-1,2,3-triazole,5-amino-1H-1,2,3-triazole, 3-amino-1H or 4H-1,2,4-triazole, 4-aminoH-1,2,4-triazole and 5-amino-1H-1,2,4-triazole and their mono-, di-, triand tetrasubstituted derivatives. Mono-, di-, tri- and tetrasubstitutedaminotriazoles may include, for example, alkyl, alkenyl, alkynyls, arylor arylalkyl groups. In some embodiments the mono-, di- tri- andtetrasubstituted aminotriazoles may include lower alkyl, lower arylalkyland aryl groups, wherein the lower alkyl and lower arylalkyl and arylgroups are defined as previously. Monosubstituted aminotriazoles mayinclude species substituted at the triazole ring and compoundssubstituted at the amino group. Disubstituted aminotriazoles may includecompounds substituted at the triazole ring and amino group, compoundsdisubstituted at the triazole ring and compounds disubstituted at theamino group. Trisubstituted aminotriazoles may include speciesdisubstituted at the triazole ring and monosubstituted at the aminogroup and compounds monosubstituted at the triazole ring anddisubstituted at the amino group.

The tetrazoles may include, for example, the 1H- and 2H-tautomers andtheir mono- or disubstituted derivatives. Monosubstituted derivativesmay include species substituted at the 1-H or 2-H position on thetetrazole ring or 1H- or 2H-tetrazoles substituted at position 5, i.e.the carbon ring atom. Disubstituted derivatives may include 1,5- or2,5-disubstituted compounds. Monosubstituted and disubstitutedderivatives may include alkyl, alkenyl, alkynyl or arylalkyl or arylgroups. The alkyl, alkenyl and alkynyl groups may be branched orunbranched, substituted or unsubstituted. In some embodiments, the mono-and disubstituted derivatives may include lower alkyl, lower aryl andarylalkyl groups. Lower alkyl and lower arylalkyl groups denote alkylgroups and alkyl moiety in arylalkyl groups having up to and including4, carbon atoms. Lower alkyls may include, for example, methyl, ethyl,propyl, isopropyl, butyl, isobutyl, secondary butyl or tertiary butyl.Lower arylalkyl, may include, for example, benzyl. Aryl groups, forexample, may include phenyl and phenyl substituted by up to andincluding 3 lower alkyl groups as defined above.

The aminotetrazoles may include, for example, 1-amino-1H-tetrazole,2-amino-2H-tetrazole, 5-amino-1H-tetrazole and 5-amino-2H-tetrazole andtheir monosubstituted, disubstituted and trisubstituted derivatives.Mono-, di- and trisubstituted aminotetrazoles may include, for example,alkyl, alkenyl, alkynyl, arylalkyl or aryl groups. The alkyl, alkenyland alkynyl groups may be branched or unbranched, substituted orunsubstituted. In some embodiments, the mono-, di- and trisubstitutedaminotetrazoles may include lower alkyl, lower aryl and arylalkylgroups. Lower alkyl and lower arylalkyl groups denote alkyl groups andalkyl moiety in arylalkyl groups having up to and including 4 carbonatoms. Lower alkyls may include, for example, methyl, ethyl, propyl,isopropyl, butyl, isobutyl, secondary butyl or tertiary butyl. Lowerarylalkyl, may include, for example, benzyl. Aryl groups, for example,may include phenyl and phenyl substituted by up to and including 3 loweralkyl groups as defined above. Monosubstituted aminotetrazoles mayinclude species substituted at the tetrazole ring or compoundssubstituted at the amino group. The disubstituted aminotetrazoles mayinclude compounds substituted at the tetrazole ring and amino group andcompounds disubstituted at the amino group.

Salts of triazoles, aminotriazoles, tetrazoles and aminotetrazolesinclude inorganic salts, for example, ammonium, aluminium; alkali metalsalts, for example, lithium, sodium or potassium; alkaline earth metalsalts, for example, calcium or magnesium; and organic salts, forexample, quaternary ammonium salts.

Some such compounds may not work in all embodiments, as determined byroutine functional testing. The utility of such compounds may, forexample, be routinely assayed in accordance with the guidance providedherein, including the Examples set out herein in which alternativenitrogen compounds may be substituted for routine test purposes.

In another aspect, the electrolyte may function as or further comprise acathode depolariser reactant to suppress cathodic hydrogen generation.The cathode depolarizer may include, for example, isonicotinic acid andsoluble salts thereof (alkali or ammonium for example), nitro-ethanol,nitromethane, nitroguanidine, nitrate salts and chlorate salts.

The invention also provides electrolytic cells incorporating anelectrolyte comprising an active nitrogen compound selected from thegroup consisting of triazoles, aminotriazoles, tetrazoles, andaminotetrazoles wherein the active nitrogen compound is an anodereactant. In some embodiments, the electrolyte may also function as orcomprise a cathode depolariser. The cathode depolariser may include, forexample, isonicotinic acid and soluble salts thereof such as alkali orammonium salts for example, nitro-ethanol, nitromethane, nitroguanidine,nitrate salts and chlorate salts.

The electrolytic cells may be associated with a fluid dispenser actuatedby nitrogen gas produced at the anode by electrolysis of the activenitrogen compounds of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing plots of volume of gas and current generatedas a function of time by electrolyte systems in PVC BUDGET-LUBER™ cellsaccording to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In one aspect, the present invention relates to the discovery that azolecompounds having a high nitrogen content may be efficiently anodicallyoxidized to generate nitrogen gas. The generation of nitrogen byelectrolysis of suitable triazoles, aminotriazoles, tetrazoles,aminotetrazoles and their respective salts may be particularly useful inelectrochemical driven fluid dispensers. The electrolytes of the presentinvention may be used in fluid dispensers actuated by nitrogen gasproduced electrochemically, such as fluid dispensers described forexample in U.S. Pat. No. 6,299,743.

In accordance with one aspect of the present invention, an electriccurrent is passed through an electrolyte comprising an active nitrogencompound selected from the group of triazoles, aminotriazoles,tetrazoles, aminotetrazoles, and their salts, the electrolyte being incontact with an anode. The electrolyte may be adapted to be sufficientlyviscous or solid to operate in combination with a permeable cathode oranode to allow gas to be evolved from it, but to prevent loss ofelectrolyte. In some embodiments, it may be desirable to have a cathodewith a high specific surface area (ie. porous or roughened) to give alow real current density on the cathode. A low cathode current densityis generally desirable for use with a cathode depolariser as it improvesthe selectivity of electro-reduction of the cathode depolarizer overelectro-reduction of water to hydrogen. The electrolyte may besufficiently liquid to permit adequate mass transfer to provide for adesired rate of gas evolution. A variety of absorbent materials orgelling agents may be used to stabilise the electrolyte against leakage,including hydrophilic absorbent materials such as cellulose sponges,cotton wool, synthetic felts, diatomaceous earth; and gelling agentssuch as Carbopol, carboxymethylcellulose and others.

The electrolyte should have sufficient conductivity to conduct theelectrolysis current. In some embodiments, the electrolyte may beprovided by the active nitrogen compound dissolved in a suitable solventor mixture of solvents. For example, 5-amino-tetrazole potassium salt isvery soluble in water and is a suitable electrolyte for carrying theelectrolytic generation of nitrogen gas. In other embodiments, asupporting electrolyte may be added to provide or enhance conductivity.A “supporting electrolyte” is defined herein as an electrolyte capableof carrying electric current but not discharging under electrolyticconditions. It is desirable in the present invention to select asupporting electrolyte that does not discharge substantially at theanode, since production of nitrogen occurs at the anode. In general, asupporting electrolyte is an ionic compound (salt, acid or base) capableof mediating electrical conductivity. Examples of suitable supportingelectrolytes may include soluble halide, sulphate, nitrate, and chloratesalts and combinations thereof, having a cation selected from the groupconsisting of lithium, sodium, potassium, calcium, magnesium, ammonium,and aluminium or quaternary-ammonium salts.

In some embodiments, the supporting electrolyte may be selected to giveelectrolyte solutions with low freezing point, for example below −20° C.In other embodiments, the supporting electrolyte may be selected to workin a pH ranging from about 4 to about 10. In some embodiments, thesupporting electrolyte may also function as a cathode depolarizer. Forexample, sodium nitrate may be used as both a supporting electrolyte anda cathode depolariser.

The supporting electrolyte may also provide antifreeze properties. Insome embodiments, antifreeze properties may be associated with the useof inorganic supporting electrolytes such as sodium chloride, calciumchloride, sulphuric acid or ammonium sulphate. An organic antifreezeagent may also be added to the electrolyte to depress its freezingpoint. In some embodiments, examples of organic antifreezes may includeacetone, glycerol, ethylene glycol, dimethyl sulphoxide, methanol,ethanol or urea. In some embodiments, the organic anti-freeze agent mayalso act as a co-solvent. For example DMSO may be used as both anantifreeze and co-solvent for 5-amino-1H-tetrazole in an aqueouselectrolyte solution where the electrolyte is the potassium salt of5-amino-tetrazole.

Suitable electrolyte solvents may be polar solvents capable ofdissolving salts such as potassium 5-amino-tetrazole for example, ororganic solvents which dissolve the non-ionic organic reactants such asthe 5-amino-1H-tetrazole for example. In some embodiments, it may bedesirable to select a solvent that provides sufficient reactantsolubility, for example greater than 1M; has a reasonably low vapourpressure, for example lower than 10 kPa at 20° C.; gives solutions withlow freezing point, for example below −20° C.; is stable againstelectro-oxidation at the anode; and is stable against electro-reductionto undesirable products which may foul the cathode or be oxidised at theanode in preference to the anode reactant. In other embodiments, thesolvent or mixture of solvents may be used to function as a non-aqueouselectrolyte.

In some embodiments, a co-solvent may be added to dissolve the activenitrogen compound in circumstances where only the supporting electrolyteis compatible with the solvent chosen to carry out the electrolyticprocess. An organic solvent may be used as a co-solvent to bringnon-ionic reactants into solution, with a polar solvent supporting theelectrolyte. For example, 5-amino-1H-tetrazole has a low solubility inwater (inferior to 1% in weight) and does not provide electricalconductivity. In order to produce nitrogen gas by electrolysis in waterof 5-amino-1H-tetrazole, dimethylsulfoxide (DMSO) may be added as aco-solvent and sodium nitrate may be added as a supporting electrolyte.In some embodiments, the co-solvent may also be a cathode reactant butit is preferable that the co-solvent not be an anode reactant.

The electrolytes of the present invention may be used in a variety ofconventional electrolysis cells, of either the one-compartment(undivided cell) or two-compartment (divided cell) type. Such cellscomprise a container capable of resisting action of electrolytes, and ananode and cathode of electronically conductive materials, which areconnected to a source of electric current. A divided electrolysis cellis one, which contains a separator that partitions the electrolytesolution to form separate anode and cathode chambers. The separator isin general a mechanical barrier, which is relatively inert to theelectrolyte, for example, a porous diaphragm such as glass-frit or anion-exchange membrane such as a NAFION™-type membrane. The anode andcathode chambers communicate through electrolyte in the pores of theseparator, which allows ion transfer but suppresses electrolyteconvection. In some embodiments, an undivided cell may preferably beemployed.

Suitable materials for the anode and the cathode may include graphitecloth, graphite felt, graphite paper, GRAFOIL™ (graphite sheet), polymerimpregnated graphite fibre and/or particles, stainless steel, nickel,DSA (noble metal oxide coated titanium) and platinised titanium. In someembodiments, it may not be necessary for the cathode to be relativelyinert.

When undivided electrolysis cells are employed, additives may be used inthe electrolyte to facilitate the generation of nitrogen at the anodewhile suppressing the co-generation of hydrogen on the cathode. Atypical cathode reaction in an undivided cell is the generation ofhydrogen by electro-reduction of water:2H₂O+2e ⁻→H₂+2OH  reaction 2

Hydrogen is however an undesirable product in some devices, such ascertain lubricant dispensers, for the reasons discussed in thebackground section herein. It may accordingly be useful to use additivesin an electrolyte that will react preferentially at the cathode tosuppress the evolution of hydrogen, such compounds are termed herein“cathode depolarisers”. In some embodiments, preferred cathodedepolarisers will not be reduced to products that suppress the evolutionof nitrogen at the anode.

In various embodiments, the invention provides a variety of alternativecathode depolarisers, such as isonicotinic acid and its soluble salts(for example, ammonium, potassium, sodium); nitroguanidine,nitro-ethanol, nitromethane, soluble nitrate salts such as ammoniumnitrate, lithium nitrate, sodium nitrate, potassium nitrate, and calciumnitrate; soluble chlorate salts such as sodium chlorate, and potassiumchlorate; and ketones such as acetone. The performance of candidatecathode depolarisers may be determined empirically in the context of aparticular electrolytic cell. Preferred depolarisers may be obtainedwhere the electro-reduction at the cathode is substantiallyirreversible. Some depolarisers may not work well under some conditions,such as a low temperature (for example below −25° C.).

In some embodiments, the electrolyte may also include one or morepromoters. The promoter may be a catalyst that increases the rate and/orselectivity of electro-oxidation of the active nitrogen compound whilepossibly also decreasing the voltage required to drive the cell at agiven current density. In some embodiments, examples of catalysts mayinclude potassium fluoride, sodium chloride, sodium bromide, silvernitrate or a complexed transition metal ion. In some embodiments, awetting agent such as sodium lauryl sulphate, sodium sulphosuccinate, orany suitable quaternary ammonium salt may be used as a promoter toimprove contact or penetration of the electrolyte with the electrode(s).In other embodiments, the promoter may be a pH buffer such as boricacid, or potassium dihydrogen phosphate that holds the electrolyte pHwithin a given range while the cell is discharged.

The invention is further illustrated by, but is not limited to, thefollowing examples.

EXAMPLE 1

This example relates to single electrode tests performed at an anodeplaced in one arm of a two-compartment H-type electrolysis cell. Table 1shows the rate of gas generated at the anode under standard conditionsfor various electrolyte solution/anode material systems. About 100 ml ofthe specified electrolyte solution is placed in one arm of a glassH-cell and subject to anodic oxidation at 0.2 Ampere on a 12 cm² anodeof the specified anode material. Calibration of the gas measuring systemis carried out by electrolysis of an aqueous solution of potassiumcarbonate (first row in Table 1). TABLE 1 Single Electrode Tests in anH-Cell. Gas Generation at the ANODE Gas generation mole/ Electrolytesolution Anode material ml STP/min Faraday Water + 5 wt % Nylon ™impregnated 0.50 0.18 K₂CO₃ graphite fibre. ATS standard. Water + 10 wt% Nylon ™ impregnated 2.5 0.90 KCH₂N₅ ^(a) graphite fibre ATS standard.Water + 10 wt % DSA^(b) 2.0 0.73 KCH₂N₅ ^(a) Water + 10 wt % 20 meshnickel 2.2 0.80 KCH₂N₅ ^(a) Water + 10 wt % 10 mesh stainless 1.9 0.68KCH₂N₅ ^(a) steel Water + 10 wt % Platinised titanium 1.9 0.70 KCH₂N₅^(a) Water + 10 wt % Anode. 2.1 0.77 KCH₂N₅ ^(a) Platinised titanium 1wt % KBr (catalyst)^(a)KCH₂N₅is 5-amino-tetrazole potassium salt (MW = 123).^(b)DSA = noble metal oxide coated titanium

When potassium carbonate solutions are electrolysed the anode gas isonly oxygen from the oxidation of water. Table 1 shows that nitrogen gascan be generated with a stoichiometry efficiency above 0.5 mol/F byanodic oxidation of potassium 5-amino-tetrazole in aqueous solution onelectrodes of various materials. The presence of a nitrogen anodereactant suppresses the oxidation of water to oxygen, but may noteliminate it. The effectiveness of an active nitrogen anode reactant atpreventing the co-generation of oxygen may depend on factors such as itsnature, its concentration, the current density, electrode compositionand temperature.

EXAMPLE 2

This example relates to single tests at the cathode performed in atwo-compartment H-type electrolysis cell. Table 2 shows the rate of gasgenerated at the cathode under standard conditions for variouselectrolyte solution/cathode material systems. The electrolyte solutionsall contain potassium 5-amino-tetrazole and a cathode depolariser. About100 ml of the specified electrolyte solution is placed in one arm of aglass H-cell and subject to anodic oxidation at 0.2 Ampere on a 12 cm²anode of the specified anode material. TABLE 2 Single Electrode Tests inan H-Cell. Gas Generation at the CATHODE Gas generation Electrolytesolution Cathode material ml STP/min mole/Faraday Water + 3 wt %Graphite felt 0.03 0.01 KCH₂N₅ ^(a) 0.5 M strontium nitrate Water + 10wt % Graphite felt 0.12 0.04 KCH₂N₅ ^(a) 1.3% nitromethane Water + 10 wt% Graphite felt 0.12 0.04 KCH₂N₅ ^(a) 2% nitromethane Water + 10 wt %Nylon ™ .031 0.11 KCH₂N₅ ^(a) ] impregnated 7% acetone Graphite fibreATS standard Water + 10 wt % Graphite cloth 0.04 0.01 KCH₂N₅ ^(a) 1.5%nitroguanidine Water + 10 wt % Graphite cloth 0.79 0.28 KCH₂N₅ ^(a)(coppered) 3.3% sodium chlorate^(a)KCH₂N₅ is 5-amino-tetrazole potassium salt (MW = 123)

Table 2 shows that cathodic reduction of aqueous solutions of potassium5-amino-tetrazole containing a cathode depolariser gives rise tostoichiometric efficiency less than 0.5 mol/F. This result indicatesthat hydrogen generation is suppressed in these systems.

EXAMPLE 3

This example relates to combined tests to simulate processes in theundivided cell of a commercial lubricator. An Anode of GRAFOIL™ graphitesheet and a cathode of graphite cloth are placed with about 100 ml ofthe electrolyte solution specified in Table 3 in one arm of an H-typeelectrolysis cell. The specified electrolyte solution is subject tosimultaneous anodic oxidation and cathodic reduction at 0.2 Ampere on 12cm² electrodes of electrode material specified in Table 3. TABLE 3Electrodes Combined in one arm of an H-Cell. Gas Generation in anUndivided Cell Gas generation (total) ml STP/ mole/ Electrolyte solutionElectrode materials min Faraday Water^(e) Anode = GRAFOIL ™ 2.0 0.72 10wt % KCH₂N₅ ^(a) Cathode = graphite cloth 0.5 M potassium nitrate^(c)[Gas. Cathode <10% anode] Water^(e) Anode = GRAFOIL ™ 2.8 0.99 10 wt %KCH₂N₅ ^(a) Cathode = graphite cloth 0.5 M potassium nitrate^(c) [Gas.Cathode <10% anode] 10% acetone^(d) Water^(e) Anode =GRAFOIL ™ 2.0 0.7010 wt % KCH₂N₅ ^(a) Cathode = graphite cloth 3% nitromethane^(c) [Gas.Cathode = zero] 10% acetone^(d) Water^(e) Anode = GRAFOIL ™ 2.6 0.91 10wt % KCH₂N₅ ^(a) Cathode = graphite cloth 3% isonicotinic acid^(c) [Gas.Cathode <1% anode] Water^(e) Anode = GRAFOIL ™ 2.6 0.91 10 wt % KCH₂N₅^(a) Cathode = graphite cloth 3% isonicotinic acid^(c) [Gas. Cathode <1%anode] 17% glycerol^(d) Water^(e) Anode = GRAFOIL ™ 2.7 0.97 6 wt %CH₃N₅ ^(b) Cathode = graphite cloth 6% isonicotinic acid^(c) [Gas.Cathode <10% anode] 28% glycerol^(d,e) 6% sodium chloride^(f) Water^(e)Anode = GRAFOIL ™ 3.6 1.29 6 wt % CH₃N₅ ^(b) ] Cathode = graphite cloth6% sodium nitrate^(c,f) Gas comp. H₂ = 5, 28% DMSO^(d,e) N₂ = 95 vol %Water^(e) Anode = GRAFOIL ™ 2.5 0.89 6 wt % CH₃N₅ ^(b) Cathode =graphite cloth 6% nitromethane^(c) [Gas. Cathode = zero] 50% ethyleneglycol^(d,e)^(a)5-amino-tetrazole potassium salt (MW = 123).^(b)5-amino-1H-tetrazole (MW = 85).^(c)cathode depolariser.^(d)antifreeze agent.^(e)solvent.^(f)supporting electrolyte

Table 3 shows that combinations of potassium 5-amino-tetrazole or5-amino-1H-tetrazole with various cathode depolarisers, and addition ofsolvents and antifreeze agents can be electrolysed together in anundivided cell to generate gas with a stochiometric efficiency above 0.5mol/F. Visual observation of both electrodes showed the rate of gasevolution from the cathode (hydrogen) ranged from zero up to about 10%of the gas rate from the anode (nitrogen).

The probable (but unknown) amino-tetrazole anode reaction is:CH₃N₅+2H₂O—>2N₂+HCOOH+NH₄ ⁺+H⁺+2e ⁻  reaction 5

Table 3 shows that some electrolytic systems give rise to astoichiometric efficiency of gas generation near the value of 1 expectedin reaction 5.

EXAMPLE 4

This example illustrates six different combinations of electrodes andelectrolyte composition, which generate nitrogen under conditionssimilar to those of a commercial lubricant dispenser. About 25 ml of anelectrolyte solution specified in Table 4 (unit 3, 5, 7, 9, 21 or 35) isabsorbed into a cellulose sponge contained between two electrodes of anATS Electro-Luber BUDGET-LUBER™ sized sealed PVC test cell (ca. 6 cmdiameter electrodes). The cell was connected in series with two 1.6 Voltbatteries, a resistor and a switch. The current and volume of gasgenerated were monitored over a period of several weeks' operation atroom temperature. TABLE 4 Gas Generation in a sealed PVC test cellCurrent Gas generation Electrolyte solution Electrode materials microAml STP/h mole/Faraday Unit 3. Anode = GRAFOIL ™ 401 0.31 0.87 Water^(e)16 wt % KCH₂N₅ ^(a) Cathode = graphite cloth 8 wt % isonicotinicacid^(c) 20 wt % DMSO^(d) 0.5 wt % boric acid Unit 5. Anode = GRAFOIL ™343 0.23 0.75 Water^(e) 16 wt % KCH₂N₅ ^(a) Cathode = graphite cloth 8wt % sodium nitrate^(c) 20 wt % DMSO^(d) Unit 7. Anode* = Nylon ™ 4110.28 0.77 Water^(e) impregnated Graphite 6 wt % CH₃N₅ ^(b) fibre 6 wt %calcium Cathode* = Nylon  ™ nitrate^(f,c) impregnated Graphite 50 wt %DMSO^(e,d) fibre Unit 9. Anode* = Nylon ™ 355 0.19 0.85 Water^(e)impregnated Graphite 10 wt % CH₃N₅ ^(b) fibre 6 wt % sodium Cathode* =Nylon ™ nitrate^(f,c) impregnated Graphite 50 wt % DMSO^(e,d) fibre Unit21. Anode = GRAFOIL ™ 475 0.38 0.98 Water^(e) Cathode = Graphite Cloth10 wt % KCH₂N₅ ^(a) 10 wt % CH₃N₅ ^(b) 8 wt % isonicotinic acid^(c) 6 wt% lithium nitrate^(f,c) 40 wt % DMSO^(e,d) Unit 35 Anode = GRAFOIL ™ 5280.46 1.03 Water^(e) Cathode = Graphite Cloth 26 wt % KCH₂N₅ ^(a) 10 wt %isonicotinic acid^(c) 40 wt % DMSO^(d)^(a)5-amino-tetrazole potassium salt (MW = 123).^(b)5-amino-1H-tetrazole (MW = 85).^(c)cathode depolariser.^(d)antifreeze agent.^(e)solvent.^(f)supporting electrolyte.*Standard A.T.S. Electro-Lube, BUDGET-LUBER ™ electrodes.

Unit 3, 5 and 35 use 5-amino-tetrazole potassium salt as anode reactant,with GRAFOIL™ (anode) and graphite cloth (cathode) electrodes and testthe effect of cathode depolariser (i.e. isonicotinic acid and sodiumnitrate). The results of these two unit runs show that potassium5-amino-tetrazole is a useful anode reactant for generating nitrogengas, since the stoichiometric efficiency for nitrogen gas ranges from0.75 to 0.85 mole of nitrogen gas per Faraday, compared to the value of1 mole/F predicted by reaction 5. Both isonicotinic acid and sodiumnitrate are effective cathode depolarisers since the hydrogen content ofthe gas produced in these units by reaction 2 was nearly nil in thefirst few days of each run and below 5% at later stages of the runs. Forboth units, the relatively high stoichiometric efficiency indicates thatsecondary anode reactions, such as oxygen generation (reaction 1), andoxidation of cathode reaction products (which in an undivided cell wouldtransport to the anode) are occurring at tolerably low rates. The lossof nitrogen gas efficiency due to secondary reactions is a majorpotential problem in practical systems, a problem that usually increasesover time, as the anode reactant is depleted and the cathode reactionproducts accumulate in the cell.

Units 7 and 9 use 5-amino-1H-tetrazole as anode reactant and standardcommercial ATS electrodes consisting of Nylon™ impregnated with graphitefibres. A greater amount of DMSO is required than in units 3 and 5 dueto the much lesser solubility of the aminotretrazole. One advantage ofusing DMSO is that it provides antifreeze properties as well. Thepresence of nitrate salts in units 7 and 9 provides the electricalconductivity necessary to conduct the electrolysis current. The standardATS electrodes and current densities used in Unit 7 and 9 runs allow thenitrate salts to act as cathode depolarisers by reduction of NO₃.

Unit 21 uses a mixture of 5-amino-tetrazole potassium salt and5-amino-1H-tetrazole as anode reactant with GRAFOIL™ (anode) andgraphite cloth (cathode) electrodes. The results of this unit show thatmixtures of high nitrogen content azole derivatives also provide usefulanode reactants for generating nitrogen gas.

EXAMPLE 5

This example gives the gas composition for different combinations ofelectrodes and electrolyte systems operating under the same experimentalconditions than those described in Example 4. Gas samples were collectedfor each unit after one month of functioning at room temperature andanalysed with a M100 gas chromatograph from MTI Analytical Instruments(Freemont, Calif.) calibrated with a gas composed by volume of 80%nitrogen, 2% oxygen, 8% hydrogen, 5% methane and 5% carbon monoxide. Thegas compositions reported in Table 5 are normalised except for caseswhere the sum of the unnormalised values is less than 100% as this mayindicate the presence of gases unidentifiable by the instrument. TABLE 5Gas composition for different Electrodes/Electrolyte systems in a sealedPVC test cell. Gas composition Electrolyte solution Electrode materials[vol. %] Unit 21 Anode = GRAFOIL ™ H₂: 0 Water^(e) Cathode = CarbonCloth O₂: 5.2 10 wt % KCH₂N₅ ^(a) N₂: 94.7 10 wt % CH₃NH₅ ^(b) CH₄: 0.128 wt % isonicotinic CO: 0.004 acid^(c) 6 wt % lithium nitrate^(f,c) 40wt % DMSO^(d,e) Unit 35 Anode = GRAFOIL ™ H₂: 0.08 Water^(e) Cathode =Carbon Cloth O₂: 6.7 26 wt % KCH₂N₅ ^(a) N₂: 93.2 10 wt % isonicotinicCH₄: 0.02 acid^(c) CO: 0.012 40 Wt % DMSO^(d) Unit 9 Anode = GRAFOIL ™H₂: 9.5 Water^(e) Cathode = Carbon Cloth O₂: 5.4 10 wt % CH₃NH₅ ^(b) N₂:80 10 wt % sodium CH₄: 0.19 nitrate^(f,c) CO: 0.006 50 wt % DMSO^(d,e)Unit 11 Anode = GRAFOIL ™ H₂: 0.8 Water^(e) Cathode = Carbon Cloth O₂: 320 wt % KCH₂N₅ ^(a) N₂: 90.5 5 wt % isonicotinic CH₄: 0.2 acid^(c) CO: 00.5 wt % Boric Acid 13 wt % DMSO^(d,e) Unit 13 Anode = ATS H₂: 0Water^(e) Cathode = ATS O₂: 5.6 10 wt % CH₃NH₅ ^(b) N₂: 94 8 wt %lithium CH₄: 0.34 nitrate^(f,c) CO: 0.02 50 wt % DMSO^(d,e) Unit 16Anode = GRAFOIL ™ H₂: 9.5 Water^(e) Cathode = Carbon Cloth O₂: 8.5 16 wt% KCH₂N₅ ^(a) N₂: 81 5 wt % isonicotinic CH₄: 0.017 acid^(c) CO: 0.008 5wt % sodium nitrate^(c) 10 wt % Ethylene Glycol^(d) 20 wt % DMSO^(d)^(a)5-amino-tetrazole potassium salt (MW = 123).^(b)5-amino-1H-tetrazole (MW = 85).^(c)cathode depolariser.^(d)antifreeze agent.^(e)solvent.^(f)supporting electrolyte.

FIG. 1 shows the gas volumes and currents measured in Unit 3, 5, 7, and9 runs. FIG. 1 also shows that generation of hydrogen gas after 27 and47 days operation of Unit 3 remains low, the remainder of the gasmeasured being only nitrogen. The range of rates of gas generationcorresponds to differences in both the current efficiencies and theeffective internal cell resistance, which sets the cell current. Theeffective cell resistance depends on several factors, such as theelectrolyte conductivity and the kinetics of the electrode reactions andthese factors are all varied in the set of Units 3, 5, 7, and 9. Thelinearity of gas generation and relative constancy of each of thecurrents with time show that the anode reaction efficiency is not muchreduced by secondary reactions arising from accumulation of cathodereaction products. A constant gas generation rate is important forcommercial applications such as lubricant dispenser, where a constantrate of grease delivery is nearly always required.

Although various embodiments of the invention are disclosed herein, manyadaptations and modifications may be made within the scope of theinvention in accordance with the common general knowledge of thoseskilled in this art. Such modifications include the substitution ofknown equivalents for any aspect of the invention in order to achievethe same result in substantially the same way. Numeric ranges areinclusive of the numbers defining the range. In the specification, theword “comprising” is used as an open-ended term, substantiallyequivalent to the phrase “including, but not limited to”, and the word“comprises” has a corresponding meaning. Citation of references hereinshall not be construed as an admission that such references are priorart to the present invention. All publications, including but notlimited to patents and patent applications, cited in this specificationare incorporated herein by reference as if each individual publicationwere specifically and individually indicated to be incorporated byreference herein and as though fully set forth herein. The inventionincludes all embodiments and variations substantially as hereinbeforedescribed and with reference to the examples and drawings.

1. An electrolyte for producing nitrogen gas by electrolysis, saidelectrolyte comprising an active nitrogen compound selected from thegroup consisting of triazoles, aminotriazoles, tetrazoles,aminotetrazoles and salts thereof, wherein said active nitrogen compoundis an anode reactant.
 2. The electrolyte of claim 1, further comprisinga cathode depolariser to suppress hydrogen gas formation.
 3. Theelectrolyte of claim 2, wherein the cathode depolariser is selected fromthe group consisting of isonicotinic acid and soluble salts thereof,nitro-ethanol, nitromethane, nitroguanidine, nitrate salts and chloratesalts.
 4. The electrolyte of claim 3, wherein the cathode depolariser isnitro-ethanol, nitromethane, isonicotinic acid, a nitrate salt or achlorate salt.
 5. The electrolyte of claim 1, wherein the electrolytecomprises an ionic compound selected from the group consisting of5-amino-tetrazole potassium, nitrate salts, chlorate salts, and chloridesalts.
 6. The electrolyte of claim 1, further comprising a co-solvent.7. The electrolyte of claim 6, wherein the co-solvent is selected fromthe group consisting of acetone, or dimethylsulphoxide, glycerol,ethylene glycol, methanol and ethanol.
 8. The electrolyte of claim 1,wherein the electrolyte comprises a supporting electrolyte.
 9. Theelectrolyte of claim 8, wherein the supporting electrolyte is a nitratesalt, a chlorate salt or a chloride salt.
 10. The electrolyte of claim1, further comprising an antifreeze agent.
 11. The electrolyte of claim10, wherein the antifreeze agent is selected from the group consistingof acetone, glycerol, DMSO, and ethylene glycol.
 12. The electrolyte ofclaim 1, wherein the active nitrogen compound is 5-amino-1H-tetrazole.13. The electrolyte of claim 2, wherein the active nitrogen compound is5-amino-1H-tetrazole.
 14. The electrolyte of claim 12, wherein theelectrolyte is aqueous and further comprises a co-solvent and asupporting electrolyte.
 15. The electrolyte of claim 14 wherein theco-solvent is glycerol, ethylene glycol or DMSO and the supportingelectrolyte is a chloride or nitrate salt.
 16. The electrolyte of claim1, wherein the active nitrogen compound is an aminotetrazole salt. 17.The electrolyte of claim 16, further comprising a cathode depolariser.18. The electrolyte of claim 17 wherein the cathode depolariser isisonicotinic acid or nitrate salt.
 19. An electrolytic cell forproducing by nitrogen gas electrolysis, comprising: (a) an anode; (b) acathode; and (c) an electrolyte comprising an active nitrogen compoundselected from the group consisting of triazoles, aminotriazoles,tetrazoles, aminotetrazoles and salts thereof, wherein said activenitrogen compound is an anode reactant.
 20. The electrolytic cell ofclaim 19, wherein the active nitrogen compound is an aminotetrazole oran aminotetrazole salt.
 21. The electrolytic cell of claim 19, furthercomprising a cathode depolariser to suppress hydrogen formation at thecathode.
 22. The electrolytic cell of claim 21, wherein the cathodedepolariser is nitro-ethanol, nitromethane, isonicotinic acid, a nitratesalt or a chlorate salt.
 23. The electrolytic cell of claim 19, furthercomprising a co-solvent.
 24. The electrolytic cell of claim 19, furthercomprising an antifreeze agent.
 25. The electrolytic cell of claim 24,wherein the antifreeze agent is acetone, glycerol, ethylene glycol, orDMSO.
 26. The electrolytic cell of claim 19, wherein the anode and thecathode comprise a polymer impregnated graphite, GRAFOIL™, graphitepaper, graphite felt or graphite cloth.
 27. The electrolytic cell ofclaim 19, wherein the active nitrogen compound is the aminotetrazole5-amino-1H-tetrazole.
 28. The electrolytic cell of claim 27, wherein thecathode depolariser is an alkali or alkaline earth nitrate salt and aco-solvent is DMSO.
 29. The electrolytic cell of claim 28, wherein theanode and the cathode are polymer impregnated graphite.
 30. Theelectrolytic cell of claim 19, wherein the active nitrogen compound isthe aminotetrazole salt potassium 5-amino-tetrazole.
 31. Theelectrolytic cell of claim 30, wherein the anode is GRAFOIL™ and thecathode is graphite cloth.
 32. The electrolytic cell of claim 31,wherein a cathode depolariser is isonicotinic acid or an alkali orammonium salt thereof, or an alkali or alkaline earth nitrate salt. 33.The electrolytic cell of claim 32 further comprising an antifreezeagent.
 34. The electrolytic cell of claim 19, wherein the anode isGRAFOIL™, the cathode is graphite cloth, and the electrolyte is anaqueous solution comprising 10% by weight of potassium5-amino-tetrazole, 10% by weight of 5-amino-1H-tetrazole, 8% by weightof isonicotinic acid, 6% by weight of lithium nitrate and 40% by weightof dimethylsulphoxide.
 35. The electrolytic cell of claim 19, whereinthe anode and cathode are Nylon™ impregnated graphite, and theelectrolyte is an aqueous solution comprising 26% by weight of potassium5-amino-tetrazole, 10% by weight of isonicotinic acid and 40% by weightof dimethylsulphoxide.
 36. The electrolytic cell of claim 19, furthercomprising a transducer for capturing the nitrogen gas generated at theanode and producing mechanical energy therefrom.
 37. The electrolyticcell of claim 36, wherein the transducer is mechanically coupled to afluid dispenser so that a fluid is dispensed from the fluid dispenserwhen nitrogen gas is generated at the anode.